The present invention relates to a circularly polarized wave plane antenna which is small in size and has a good (lower) axial ratio characteristic over a broad frequency range, and is constructed with a dielectric plane antenna and a 90xc2x0 phase adjusting circuit (hereafter referred to as a 90xc2x0 hybrid).
In most of circularly polarized wave antennas of the prior art by means of dielectric plane antennas using patch electrodes, typically one-point feeding technique has been employed and frequency ranges exhibiting good axial ratio have been limited. GPS has a center frequency of 1575.42 MHz and a relatively narrow fractional band width of 0.13% for a frequency range of xc2x11.023 MHz around it, and accordingly there has not been required to extend the frequency range with good axial ratio. As a result, no problem has arisen with a micro strip circularly polarized wave antenna of one-point feeding.
However, as much higher frequency ranges have been used in communications and broadcastings, the fractional band width, for example, for a radio LAN using ISM band of 2450 MHzxc2x150 MHz has become 4.1%, and thereby there has arisen a need to extend a good axial ratio-frequency range.
Conventionally, a circularly polarized wave antenna employing a 90xc2x0 hybrid has been uncommonly used for the purpose where the only one element is used. In order to obtain an antenna having a narrower directivity with higher gain, a number of radiation electrodes and the 90xc2x0 hybrids have usually been arranged on the same face, as shown in FIG. 1, in an antenna array of such a configuration as shown in FIG. 2. As a result, the 90xc2x0 hybrids have turned to occupy a larger area than the radiation electrodes, which means that it is not suitable for miniaturization.
The present invention has been made to provides a miniaturized circularly polarized wave plane antenna which may be used not only in a radio LAN of 2450 MHz band but also in communications requiring good axial ratio over broad band areas, such as a 5150-5250 MHz band radio LAN and a 5250-5350 MHz band radio access, a 5795-5845 MHz band ETC, a satellite digital broadcasting and the like.
The present invention has overcome the above problems by providing a novel structure, in which a dielectric plane antenna element and a 90xc2x0 hybrid are placed one on the other so that the 90xc2x0 hybrid may be accommodated in the back face of the dielectric plane antenna element. Further, the present invention is made to improve the property thereof by improving a connection structure of the 90xc2x0 hybrid with a coaxial line as well as with the antenna element.
A plane antenna according to the present invention has a 90xc2x0 hybrid which has a grounding face of a plane antenna element formed in a surface of a printed substrate as a 90xc2x0 hybrid, and a conductor pattern having one wave length in one circle and an earth pattern respectively formed in a back face of the printed substrate, respectively, and the antenna element is arranged over the grounding face.
As for a connection and a layout of the coaxial line with respect to the conductor pattern and the earth pattern, if the coaxial line is directly derived outwardly from the connection point, a balance between resonant frequencies in the X- and the Y-directions could be lost leading to a reverse affection to the axial ratio characteristics in the circularly polarized wave property. The present invention provides a circularly polarized wave plane antenna which allows the balance between the resonant frequencies in the X- and the Y-directions to be hardly lost and exhibits a good and stable axial ratio characteristics in the circularly polarized wave property.
More specifically, the present invention provides a novel plane antenna comprising: a dielectric plane antenna element using a resonance mode of two axial directions orthogonally passing through a center point of a conductor pattern arranged on a dielectric substrate and having a feeding point at a 50xcexa9 matching point on each of the axial lines; and a 90xc2x0 hybrid comprising a closed conductor pattern having one wave length in one circle, which includes two ports for connecting said closed conductor pattern with each of said feeding points, and two coaxial line connecting ports, at least one of which is connected to a transmitting or receiving circuit, said plane antenna characterized in that: said 90xc2x0 hybrid is formed into a wiring board having not less than two layers; said two ports to be connected to said feeding points are drawn out toward an inside of said closed conductor pattern; and an earth pattern is formed surrounding said closed conductor pattern, wherein said inwardly drawn out ports are connected with said feeding points; one of said ports of said closed conductor pattern and said earth pattern are connected with a core line and a sheath line of a coaxial line respectively; and said 90xc2x0 hybrid is disposed in a back face of said dielectric plane antenna element.
Further, the present invention provides another novel plane antenna comprising: a dielectric plane antenna element using a resonance mode of two axial directions orthogonally passing through a center point of a conductor pattern arranged on a dielectric substrate and having a feeding point at a 50xcexa9 matching point on each of the axial lines; and a 90xc2x0 hybrid comprising a closed conductor pattern having one wave length in one circle, which includes two ports for connecting said closed conductor pattern with each of said feeding points and two coaxial line connecting ports, at least one of which is connected to a transmitting or receiving circuit, said plane antenna characterized in that: said 90xc2x0 hybrid is formed into a wiring board having not less than two layers; said two ports to be connected to said feeding points are drawn out toward an inside of said closed conductor pattern; and an earth pattern is formed surrounding said closed conductor pattern, wherein said inwardly drawn out ports are connected with said feeding points; one of said ports of said closed conductor pattern and said earth pattern are connected with a coaxial line respectively at central locations on a side of said closed conductor pattern; and said 90xc2x0 hybrid is disposed in a back face of said dielectric plane antenna element.
Still further, the present invention provides another novel plane antenna comprising: a dielectric plane antenna element using a resonance mode of two axial directions orthogonally passing through a center point of a conductor pattern arranged on a dielectric substrate and having a feeding point at a 50xcexa9 matching point on each of the axial lines; and a 90xc2x0 hybrid comprising a closed conductor pattern having one wave length in one circle, which includes two ports for connecting said closed conductor pattern with each of said feeding points and two coaxial line connecting ports, at least one of which is connected to a transmitting or receiving circuit, said plane antenna characterized in that: said 90xc2x0 hybrid is formed into a wiring board having not less than two layers; said two ports to be connected to said feeding points are drawn out from locations approximately on a diagonal line of said wiring board of said closed conductor pattern toward an inside thereof; and an earth pattern is formed surrounding said closed conductor pattern, wherein said inwardly drawn out ports are connected with said feeding points; one of said ports of said closed conductor pattern and said earth pattern are connected with a core line and a sheath line of a coaxial line respectively at locations approximately on a diagonal line of said wiring board; the other port not to be connected to the feeding point nor to the coaxial line is connected to the earth pattern via an impedance element; and said 90xc2x0 hybrid is disposed in a back face of said dielectric plane antenna element.
According to another aspect, the present invention provides another novel plane antenna comprising: a dielectric plane antenna element using a resonance mode of two axial directions orthogonally passing through a center point of a conductor pattern arranged on a dielectric substrate and having a feeding point at a 50xcexa9 matching point on each of the axial lines; and a 90xc2x0 hybrid comprising a closed conductor pattern having one wave length in one circle, which includes two ports for connecting said closed conductor pattern with each of said feeding points and two coaxial line connecting ports, at least one of which is connected to a transmitting or receiving circuit, said plane antenna characterized in that: said 90xc2x0 hybrid is formed into a wiring board having not less than two layers; said two ports to be connected to said feeding points are drawn out toward an inside of said closed conductor pattern; and an earth pattern is formed inside said closed conductor pattern, wherein said inwardly drawn out ports are connected with said feeding points; one of said ports of said closed conductor pattern and said earth pattern are connected with a core line and a sheath line of a coaxial line respectively; and said 90xc2x0 hybrid is disposed in a back face of said dielectric plane antenna element.
Still further, the present invention provides another novel plane antenna comprising: a dielectric plane antenna element using a resonance mode of two axial directions orthogonally passing through a center point of a conductor pattern arranged on a dielectric substrate and having a feeding point at a 50xcexa9 matching point on each of the axial lines; and a 90xc2x0 hybrid comprising a closed conductor pattern having one wave length in one circle, which includes two ports for connecting said closed conductor pattern with each of said feeding points and two coaxial line connecting ports, at least one of which is connected to a transmitting or receiving circuit, said plane antenna characterized in that: said 90xc2x0 hybrid is formed into a wiring board having not less than two layers; said two ports to be connected to said feeding points are drawn out toward an inside of said closed conductor pattern; and an earth pattern is formed into an island-like shape inside said closed conductor pattern, wherein said inwardly drawn out ports are connected with said feeding points; one of said ports of said closed conductor pattern and said earth pattern are connected with a core line and a sheath line of a coaxial line respectively at a central location on an edge of said closed conductor pattern; and said 90xc2x0 hybrid is disposed in a back face of said dielectric plane antenna element.
Yet further, the present invention provides another novel plane antenna comprising: a dielectric plane antenna element using a resonance mode of two axial directions orthogonally passing through a center point of a conductor pattern arranged on a dielectric substrate and having a feeding point at a 50xcexa9 matching point on each of the axial lines; and a 90xc2x0 hybrid comprising a closed conductor pattern having one wave length in one circle, which includes two ports for connecting said closed conductor pattern with each of said feeding points and two coaxial line connecting ports, at least one of which is connected to a transmitting or receiving circuit, said plane antenna characterized in that: said 90xc2x0 hybrid is formed into a wiring board having not less than two layers; said two ports to be connected to said feeding points are drawn out from locations on a diagonal line of the wiring board toward an inside of said closed conductor pattern; and an earth pattern is formed into an island-like shape inside said closed conductor pattern, wherein said inwardly drawn out ports are connected with said feeding points; one of said ports of said closed conductor pattern and said earth pattern are connected with a core line and a sheath line of a coaxial line respectively at the locations approximately on a diagonal line of the wiring board; the other port not to be connected to the feeding point nor to the coaxial line is connected to the earth pattern via an impedance element; and said 90xc2x0 hybrid is disposed in a back face of said dielectric plane antenna element.
Components of a plane antenna according to the present invention are as follows:
A dielectric plane antenna element comprising a square or circular patch which includes a radiation electrode equipped with two feeding points on matching locations in two axial directions;
a wiring board of not less than two layers, on which a 90xc2x0 hybrid and a conductor pattern serving as a port for said 90xc2x0 hybrid are formed, wherein a conductor formed on one surface operates as a grounding electrode of the antenna, and on the other surface, there are provided a 90xc2x0 hybrid made up of closed conductor pattern having one wave length in one circle, two ports drawn out toward an inside of the closed conductor pattern for connecting respective feeding points, and two coaxial line connecting ports to be connected to a transmitting or receiving circuit and an earth pattern surrounding the closed conductor pattern or another earth pattern formed inside the closed conductor pattern; and
a coaxial line to be connected to the port of the 90xc2x0 hybrid and the earth pattern.
An impedance matching connection of the port not to be coupled with the coaxial line and the earth pattern may be accomplished by a resistor of 50xcexa9 or by the pattern on the wiring board.
The characteristics of the antenna may be improved by guiding the coaxial line from the center point of one side of the closed conductor pattern across the closed conductor pattern, or from one corner of the closed conductor diagonally across the closed conductor pattern, so as to be drawn outside of the wiring board.